1-(2-Aminoethyl)imidazolidin-2-one (hereinafter, UDETA) is a compound, corresponding to the following formula:
which has the advantage of having not only a reactive primary amine function that makes it possible to envision its condensation on numerous carbonyl derivatives, but also free electron doublets capable of producing hydrogen bonds between the molecules onto which it is grafted or between these molecules and other molecules bearing associative groups. UDETA is thus used, in particular, for the synthesis of supramolecular materials (FR2924715). The applicant has also proposed using UDETA as a salifying agent, for producing a styrene/maleic anhydride copolymer-based additive intended for coating or sizing paper (FR2925504). UDETA is also involved in the production of pharmaceutical compounds (as described, in particular, in WO 2009/142569, US 2009/270372, WO 2009/114566 and WO 2009/138438), of phytosanitary products, in particular pesticides, or of additives for paints or lubricants (U.S. Pat. No. 5,746,946).
U.S. Pat. No. 2,613,212 is one of the first to describe the synthesis of UDETA. In said document, it is indicated that UDETA can be obtained by reacting at least one mole of diethylenetriamine (or DETA) with one mole of urea, and preferably an equimolar amount of these reactants, at a temperature of from 100 to 300° C. In the examples of said document, the molar ratio of the DETA to the urea is abut 1.2. The mixture is heated to 210 or 250° C. The product obtained is then distilled under reduced pressure at 155-163° C. An application of this process is illustrated in example 1 of U.S. Pat. No. 5,746,946 probably, using a DETA:urea molar ratio of 1:1 and using reaction and distillation temperatures of at most 150° C. It is indicated in said document that the product obtained has a purity of 95%. However, the inventors have demonstrated, by reproducing this example, that it results in a product containing approximately 63% of UDETA only. The difference with the value indicated in U.S. Pat. No. 5,746,946 comes from the fact that, in said patent, the purity is defined in terms of an alkalinity measurement, which is not sufficient to exclude the presence of impurities containing amine functions and themselves generating a certain alkalinity.
In an analogous manner, U.S. Pat. No. 4,491,527 (example 2) has described a process for synthesizing UDETA using a mixture of DETA and urea in a DETA:urea molar ratio of 2:1, which is brought to 203° C. The product obtained is then distilled under reduced pressure, at a temperature of 165-175° C.
Comparative example 1 of application DE 199 57 348 also discloses a process for synthesizing a product containing “predominantly” UDETA, from a mixture of equimolar amounts of DETA and urea, brought to 155° C. Another process of this type is illustrated by example C of application WO 97/49676. In this example, the DETA/urea molar ratio is approximately 1 and the mixture is heated to 210° C. before being distilled under reduced pressure at more than 175° C.
The UDETA obtained according to these processes contains, like the commercial UDETA used in U.S. Pat. No. 4,104,220, a significant amount of impurities. The commercially available qualities of standard UDETA thus generally have a UDETA titer of approximately 85%.
For certain applications, in particular for the synthesis of supramolecular compounds, it would, however, be desirable to be able to have available a UDETA quality having a purity of at least 90%, for example of at least 95%. In particular, if the UDETA must be used as a synthon in pharmaceutical chemistry, a purity of at least 98%, or even of at least 99%, is even sought. Moreover, it is desirable to have available a UDETA quality containing less than 5%, or even less than 3%, by weight of TETU, less than 1% by weight of DETA, less than 5% by weight of DETA-urea-DETA and/or less than 1% by weight of organic solvent.
Among the major impurities present in the UDETA obtained according to the prior art processes, mention may be made of the residual DETA, and also TETU or N,N′-bis[2-(2-oxo-1-imidazolindinyl)ethyl] and the condensation product DETA-urea-UDETA. The presence of DETA is in particular problematic in the field of the synthesis of supramolecular compounds, insofar as it has several reactive groups capable of forming undesirable bonds with the other synthons used in the synthesis of these compounds.
The means used up until now to reduce the amount of these impurities comprise in particular the purification of the UDETA by extraction in a solvent. The company King Industries thus proposes a UDETA grade which is purer than the standard grades, but which contains large amounts of solvent (about 9%) which may be prejudicial in certain applications. Another means of UDETA purification consists of distillation under vacuum or reduced pressure, which is usually carried out at a temperature greater than 150° C., and generally of at least 160° C., as previously indicated. However, the inventors have demonstrated that these distillation conditions lead to a retrogradation of the UDETA to give DETA and TETU. Specifically, the conventional vacuum distillation technique is reflected by an increase in the TETU content at the bottom of the column and by the accumulation of a UDETA/DETA mixture at the top. This retrogradation affects the purity of the UDETA, and also the reaction yield.
Supported by this observation, the inventors have subsequently demonstrated that the purity of the UDETA is also affected by the DETA:urea molar ratio, which influences the TETU content. Specifically, the lower this ratio, the larger the amount of TETU formed. Following many experiments, they have thus demonstrated that adjusting these two parameters (distillation conditions and DETA:urea ratio) in given ranges makes it possible to obtain a product that can reach a very high UDETA purity, according to a process that is simple and economical to implement, in particular in terms of energy consumption and owing to the absence of any recourse to a solvent purification step. They have also demonstrated that this process can be transposed to the preparation of the thiocarbonyl of UDETA.